Leukotriene C4 elimination and metabolism in man

Three doses of radiolabeled leukotriene C4 (0.2 to 15 muCi) were infused into three subjects to investigate its metabolism and routes of elimination during 4 days. Between 12% and 20% of the infused dose was recovered in the urine within 24 hours, of which a substantial and relatively constant proportion (4.1% to 6.3% total dose) appeared as leukotriene E4 (LTE4), mainly in the first 4 hours. Polar omega-oxidation products, N-acetyl LTE4, and tritiated water were also present. Fecal elimination accounted for a further 30% to 40% of the infused dose. In the absence of altered metabolism or biliary excretion, urinary LTE4 may be a useful measure of whole body production of the cysteinyl leukotrienes.

Capsaicin-induced bronchodilation in mild asthmatic subjects: possible role of nonadrenergic inhibitory system

We investigated whether stimulation of vagal afferent nerve fibers with inhaled capsaicin could induce a nonadrenergic inhibitory reflex in nine mild asthmatic subjects. Changes in total respiratory resistance (Rrs) were measured with a forced oscillation technique. First we induced a rise of 71 +/- 15% in Rrs (P less than 0.001) after leukotriene D4 aerosol. Subsequent inhalation of capsaicin (2 nmol) caused no significant change in mean Rrs of -1.1 +/- 8.2%. After the muscarinic receptor antagonist ipratropium bromide (120 micrograms) was inhaled, leukotriene D4 increased Rrs by 103 +/- 9% (P less than 0.001). Capsaicin subsequently caused bronchodilation in all subjects (Rrs = -22.3 +/- 2.7%, P less than 0.001). Ethanol-saline (diluent) alone caused a nonsignificant fall in Rrs (-9.9 +/- 4.7%) but a deep breath and coughing resulted in bronchodilation (-16.9 +/- 6.1%, P less than 0.05 and -11.6 +/- 2.9%, P less than 0.01, respectively). As observed in normal subjects, capsaicin may initiate an inhibitory reflex, presumably of nonadrenergic origin. This reflex could not be distinguished from that caused by coughing or by deep inhalation. A defect in nonadrenergic mechanisms, at least in mild asthma, seems unlikely.

Localization of the site of the bronchoconstrictor effects of leukotriene C4 compared with that of histamine in asthmatic subjects

Although the sulfidopeptide leukotrienes are known to be potent bronchoconstrictors, the relative aerodynamic site of response to these compounds is controversial. We determined the decrease in maximal expiratory flow rates (Vmax) from partial and maximal flow-volume curves in seven asthmatic subjects after inhalation of aerosols of histamine or leukotriene C4 (LTC4) while breathing air or a mixture of 80% helium and 20% oxygen (He/O2). Density dependence (DD) of maximal expiratory flow was determined from partial expiratory flow volume curves by an isovolumic comparison of maximal expiratory flows with subjects breathing He/O2 with those obtained while breathing air. Measurements were made before and after inhalation of aerosols generated from graded concentrations of each constrictor agent. An aerodynamic site of response to LTC4 more central than for histamine was indicated by a significant (p less than 0.02) increase in DD with the former but not with the latter agonist. The ratio of Vmax at 30% vital capacity determined from maximal and partial maneuvers (M/P) was routinely higher at baseline while breathing He/O2 compared to the corresponding values with air, suggesting a degree of peripheral obstruction that was reversed by a deep inhalation. Obstruction induced by LTC4 inhalation resulted in a greater increase in M/P compared with baseline when air was the test gas (p less than 0.02). This was not observed when He/O2 was the test gas. Similar effects on M/P were not induced by histamine aerosol inhalation, consistent with a central airway response to LTC4 that was not affected by volume history.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and metabolism of leukotriene C4 after cisternal injection in guinea pigs

Following cisternal injection of [3H8]LTC4 into guinea pigs, leukotriene metabolites were identified in the brain, cerebellum, perilymph, blood, liver and kidneys. LTC4 was metabolized into LTD4 and LTE4 in the cerebrospinal fluid and LTE4 was transported into the blood for general circulation and uptake into the liver and kidneys. The excretion of LTE4 from CNS to blood seemed to be the rate-limiting step in the elimination of leukotrienes from the body. Leukotrienes were also transported into the perilymph. The conversion of LTC4 into LTD4 and LTE4 was lower in perilymph as compared to the cerebrospinal fluid, suggesting a rate limiting function of the cochlear aqueduct that can be defined as a cerebrospinal fluid-labyrinth barrier.

Effect of the oral leukotriene D4 antagonist LY171883 on inhaled and intradermal challenge with antigen and leukotriene D4 in atopic subjects

Sulfidopeptide leukotrienes have been suggested as potential mediators of the bronchoconstriction of asthma. The effect of the orally active leukotriene D4 (LTD4) antagonist LY171883 (LY) (400 mg) on antigen or LTD4-induced bronchoconstriction and wheal-and-flare responses was studied in atopic subjects on six occasions (three groups of 2 consecutive days). On the first 2 study days, subjects were screened for their response to inhaled LTD4 and antigen. On the second and third groups of 2 study days, subjects received LY, 400 mg, or placebo 2 hours before inhaled leukotriene LTD4 or antigen challenge. After antigen challenge, the lung function was measured for 6 hours. After the inhaled challenge, intradermal LTD4 and antigen challenges were performed. LY had no effect on baseline lung function. Geometric mean (95% confidence intervals) for the provocative dose of LTD4 causing a 40% fall in forced expiratory flow at 40% vital capacity from a forced expiratory flow maneuver was 1.8 (0.5 to 5.6) nmol after placebo and 5.6 (2.0 to 15.7) nmol after LY. This difference was not significant. The mean maximum change during the early phase of antigen-induced bronchoconstriction was reduced, being 54.7 (26.9% to 82.4%) after placebo and 35.8 (2.3% to 69.3%) after LY (p less than 0.05). There was, however, no difference in the maximum response observed during the late phase. There was also a significant reduction in the area under the curve of the early but not late-phase response to antigen. LY significantly shifted the intradermal LTD4 dose-response curve for both wheal and flare to the right (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention and reversal of aerosol LTD4-induced changes in guinea pig pulmonary mechanics by Wy-48252, an orally active LTD4/E4 receptor antagonist

Anesthetized male albino guinea pigs were prepared for recording changes in the pulmonary mechanics parameters, dynamic compliance (Cdyn) and airway conductance (Gaw). Two aerosol leukotriene D4 (LTD4) challenges (0.125 microgram/ml, 3-7 breaths, 1 h apart) were administered via an ultrasonic nebulizer to each animal and, produced reductions in Cdyn that were approximately 60% of those of Gaw. Intraduodenal administration of the LTD4/E4 receptor antagonists Wy-48252 (30 min), Wy-45911 and Ly-171883 (15 min) produced dose-related inhibition of the second LTD4 challenge. From the data, ID50 values were calculated and, Wy-48252 was 8- to 17-fold more potent (mg/kg) than Wy-45911 or Ly-171883. Responses to histamine were not altered by the antagonists. In separate experiments, Wy-48252 (0.3 and 1 mg/kg i.v.) rapidly reversed aerosol LTD4-induced decreases of Cdyn and Gaw, but did not reverse pulmonary mechanics decreases produced by prostaglandin F2 alpha. The results indicate that systemically administered LTD4 receptor antagonists can both prevent and reverse bronchoconstriction produced by aerosol LTD4 in the guinea pig.

Effect of inhaled leukotriene C4 on cardiopulmonary function

The changes in transcutaneous oxygen saturation (SaO2%) and airway responses to inhaled histamine and leukotriene C4 (LTC4) were examined in 10 asthmatic patients, and the effect of inhaled LTC4 (16 nmol) on cardiopulmonary hemodynamics was examined in seven nonasthmatic patients undergoing diagnostic cardiac catheterization. In asthmatic patients, LTC4 produced oxygen desaturation on two occasions. At a lower dose (2.0 nmol) LTC4 produced a marked fall in SaO2% that lasted less than 15 min and occurred in the absence of significant bronchoconstriction as measured by changes in FEV1, FEF25-75, and SGaw. At a higher cumulative dose (7 nmol), LTC4 caused prolonged oxygen desaturation with slow recovery and this was associated with significant bronchoconstriction. In contrast, histamine inhalation produced a single response with a fall in both FEV1 and SaO2% of short duration. The dose-response characteristics of LTC4 and histamine on oxygen desaturation in asthmatic patients appear to differ significantly and probably are dependent on relative sensitivities of pulmonary vascular and bronchial smooth muscle to these agonists. A single inhaled dose of LTC4 in nonasthmatic subjects produced a marked drop in PaO2 with significant increase in AaPO2, and this was associated with a mean (SEM) decrease in FEV1 of 14% (2.5) from the baseline. The mean cardiac output fell by 15% (3.4) without significant changes in blood pressure and heart rate. There was no electrocardiographic evidence of myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bolus injections of leukotrienes and norepinephrine on forelimb vascular and lymphatic pressures

Leukotrienes, lypoxygenase metabolites of arachadonic acid, have been reported to be potent vasoconstrictors in some organs. This study was undertaken to delineate the actions of leukotrienes on both vascular and lymphatic vessels in the canine forelimb. Bolus intra-arterial injections of 1 microgram and 10 micrograms of leukotriene B4, C4, and D4 and 1 microgram of norepinephrine were made into forelimbs perfused at constant flow. Norepinephrine significantly increased systemic, forelimb perfusion and small artery pressures. Lymphatic pressure was significantly increased from a control of 6.6 mmHg to a peak of 14.4 mmHg. Leukotriene B4 in either dosage, did not significantly affect vascular or lymphatic pressures. Leukotriene C4 (1 microgram or 10 micrograms) significantly increased systemic and forelimb arterial pressures but did not alter lymphatic pressure. Leukotriene D4 (1 microgram) significantly increased small artery pressure. Leukotriene D4 (10 micrograms) increased systemic and forelimb arterial pressures. Neither dosage of leukotriene D4 significantly affected lymphatic pressure. Repeat injection of norepinephrine after completion of all leukotriene injections again markedly increased systemic, forelimb arterial and lymphatic pressures. These data indicate that leukotrienes exhibit only mild constrictor effects on forelimb blood vessels and do not significantly affect forelimb prenodal lymphatic vessels.

Conscious guinea-pig aerosol model for evaluation of peptide leukotriene antagonists

A new conscious animal model for evaluating leukotriene antagonists is described. The model consists of monitoring the change in the respiratory pattern induced by aerosol administration of various airway constrictors in six guinea pigs secured in a plexiglass chamber by a neck yoke. The animals are pretreated with indomethacin (10 mg/kg, i.p.) and propranolol (5 mg/kg, i.p.) 30 min prior to the challenge. After a 30-min stabilization period, the animals are challenged by various agonists delivered via a Monaghan ultrasonic nebulizer at a flow rate of 2.0 L/min for 5 min. The end point is defined as the onset of slow, labored abdominal breathing (dyspnea) measured in seconds. Peptide leukotrienes (LTs) (30 nM-60 microM) produced concentration-related decreases in time to dyspnea with a rank order of potency of LTD4 greater than LTC4 greater than LTE4. LTD4 was 1,000-fold more potent than histamine or carbachol. Pretreatment of the animals with either FPL55712 or LY171883 delayed the time to reach dyspnea induced by LTD4. In contrast, pyrilamine, cyproheptadine, and phenoxybenzamine failed to alter LTD4-induced dyspnea. The results indicate that this model is useful in assessing the efficacy of LT receptor antagonists in vivo.

Secondary release of thromboxane A2 in aerosol leukotriene C4-induced bronchoconstriction in guinea pigs

Effect of a thromboxane synthetase inhibitor (OKY-046) on bronchoconstriction induced by aerosol leukotriene C4 and histamine was studied in anesthetized, artificially ventilated guinea pigs in order to examine whether secondary release of thromboxane A2 is produced by aerosol leukotriene C4 or not. 0.01-1.0 micrograms/ml of leukotriene C4 and 12.5-400 micrograms/ml of histamine inhaled from ultrasonic nebulizer developed for small animals caused dose-dependent increase of pressure at airway opening (Pao) which is considered to be an index representing bronchial response. Pretreatment of the animals with intravenous OKY-046 (100mg/kg) significantly reduced the airway responses produced by inhalation of 0.1, 0.33 and 1.0 micrograms/ml of leukotriene C4, while the pretreatment did not affect the histamine dose-response curve. Based on these findings and previous reports (6,7), it is suggested that aerosol leukotriene C4 activates arachidonate cyclooxygenase pathway including thromboxane A2 synthesis and the released cyclooxygenase products have bronchodilating effect as a whole.

Synergistic effects of LTB4 and LTD4 on leukocyte emigration into the guinea pig conjunctiva

Leukotrienes (LT) B4 and D4, alone and in combination, were topically applied to the eyes of guinea pigs, and their effects on conjunctival leukocyte infiltration studied. LTD4 potentiated the neutrophil response to LTB4, even though no neutrophil emigration was evoked by LTD4 itself over a dose range of 10-1000 ng. LTB4 alone at the 1-ng and 10-ng doses failed to evoke any leukocyte emigration, but significant numbers of neutrophils were observed at these concentrations when LTD4 (1-1000 ng) was present. Although a dose-dependent increase in neutrophil infiltration was observed for the 100-ng and 1000-ng doses of LTB4, cell counts were substantially higher with these doses in the presence of LTD4. Eosinophil numbers increased in a dose-related manner in response to LTB4 and LTD4 alone, with a greater response to LTD4. The addition of either 10 ng or 100 ng of LTB4 to graded doses of LTD4 (10-1000 ng) caused increased eosinophil numbers, the lower dose of LTB4 potentiating the response to LTD4 and the higher LTB4 dose showing no significant effect. The effects on leukocyte infiltration that were evoked by the LT combinations could not be explained simply on the basis of an increase in vascular permeability. Bradykinin (BK), a potent conjunctival microvascular permeability factor that does not elicit any leukocyte infiltration, did not significantly potentiate LTB4-induced eosinophil or neutrophil emigration. The synergistic effects of LTs on leukocyte emigration are also difficult to ascribe to hyperemia (ie, increased blood volume in the conjunctiva), because both LTB4 and LTD4 caused only very modest increases in conjunctival blood content, and BK, which did not potentiate the leukocytic responses to LTB4, caused marked increases in tissue blood content. High-dose LT combinations caused eosinophils, but not neutrophils, to migrate into the conjunctival epithelium and fragment, resulting in overt tissue damage. These results further suggest a synergistic interaction between LTB4 and LTD4 that directly alters leukocyte function. The relevance of these observations to a number of disease and trauma states is discussed.

Lymphatic smooth muscle responses to leukotrienes, histamine and platelet activating factor

Regional lymphatics regulate the accumulation of edema resulting from inflammation. The effects of mediators of inflammation on lymphatic smooth muscle, the primary determinant of lymph flow, are poorly understood. We studied mesenteric lymphatic vessels in 22 anesthetized rats with in vivo videomicroscopy following topical applications of histamine, leukotriene C4 or D4, or platelet-activating factor (PAF). Diameter, contractility, and contraction frequency were measured, and flow was calculated. Histamine caused increases in vessel diameter and contractility (174 and 218% of control, respectively; P less than 0.05), while contraction frequency was unaffected. Leukotrienes C4 and D4 caused an increase in frequency of contraction (348 and 392% of control, respectively; P less than 0.05), while having no significant influence on diameter or contractility. PAF caused smooth muscle relaxation, resulting in vasodilation and a decrease in contraction frequency (202 and 5% of control, respectively; P less than 0.05). Topical application of histamine and leukotrienes caused significant increases in calculated flow, while PAF decreased calculated flow. Mediators of inflammation have striking and diverse effects on lymphatic smooth muscle activity.

The excretion of leukotriene E4 into urine following inhalation of leukotriene D4 by human individuals

Healthy volunteers underwent bronchial challenge with increasing doses of nebulized leukotriene D4 (0.007 - 200 nmol) at 15 min intervals. Total amounts of 200 nmol (females) and 400 nmol (males) were inhaled, corresponding to approximately 100 nmol and 200 nmol deposited in the lung, respectively. Of the latter amounts 3 +/- 1% (mean +/- S.E.M., n = 5) was found to be excreted as leukotriene E4 into the urine within 12 h. No further excretion after this period was observed. Approximately 50% of the total urinary leukotriene E4 was excreted during the first 2 h. These results suggest that a possible formation of sulfidopeptide leukotrienes in the lung in vivo can be monitored by measuring leukotriene E4 excretion into the urine.

Mechanism of leukotriene D4-induced bronchoconstriction in normal subject

Leukotriene (LT) D4 is a potent constrictor of human airways and a putative mediator of asthma. However, its mechanism of action in man has not been established. In the present study we sought to determine the role of upper airway reflexes, cholinergic pathways, and cyclooxygenase products of arachidonic acid metabolism in mediating LTD4-induced bronchoconstriction in man. Six normal subjects underwent bronchoprovocation testing with LTD4 after pretreatment with either aerosolized phosphate-buffered saline, aerosolized atropine (1.5 mg), aerosolized lidocaine (80 to 160 mg), or oral indomethacin (50 mg three times daily for 10 doses). Specific airway conductance (SGaw), the flow rate at 30% of vital capacity from a partial forced expiratory maneuver (V30P), and the FEV1 were measured at each concentration of LTD4. We calculated the provocative concentration of LTD4 required to produce a 35% fall in SGaw (PC35SGaw) or a 30% fall in V30P (PC30V30P) and the slope of the LTD4 dose-response curve. Atropine increased baseline SGaw 49% (p less than 0.01) and V30P 43% (p less than 0.005). Atropine also increased the PC35SGaw and PC30V30P and increased the slope of the LTD4 dose-response curve. However, neither of these opposing effects was significant. Lidocaine had no effect on either baseline function or the airway response to LTD4. Indomethacin produced small decreases in baseline V30P (12%) and FEV1 (3%) (p less than 0.05 for both), but it too had no effect on the airway response to LTD4. These results indicate that the bronchoconstriction produced by aerosolized LTD4 in normal subjects is not mediated by cyclooxygenase products of arachidonic acid metabolism or irritant receptors in the upper airways. Although cholinergic pathways may play some role, the data suggest that bronchoconstriction results, at least in part, from a direct effect of LTD4 on airway smooth muscle.

Nebulization and selective deposition of LTD4 in human lungs

The process of nebulization and deposition of LTD4 was studied in detail. The concentration of LTD4 in a saline solution decreased by approximately 90% after 2 min of nebulization in a DeVilbiss 35B ultrasonic nebulizer. This decrease was prevented by diluting LTD4 in a phosphate buffer, pH 7.4. Nebulization of tritiated LTD4 in this phosphate buffer did not cause any appreciable deterioration of the leukotriene, as demonstrated by an unchanged ratio between radioactivity and LTD4 concentration in the test solution before and after nebulization as well as in the condensed aerosol. The aerosol generated by the DeVilbiss 35B ultrasonic nebulizer was shown to generate particles with a mass median diameter of 1.3 microns (dry particle size). Interposition of a settling bag reduced the amount of large particles, reducing the mass median diameter to 0.84 microns (dry particle size). Nine healthy volunteers were challenged on separate days with 40 nmol LTD4 or 100 mumol histamine, and the changes in FEV1 and partial flow volume curves initiated at 50% of vital capacity (Vmax30) were measured. A relative diffuse deposition pattern was ensured by inhalation via a settling bag. These results were compared to challenges with a relatively central deposition pattern as ensured by inhalation directly from the nebulizer with brisk inhalation maneuvers. The diffuse deposition pattern caused minimal changes in FEV1 but pronounced effect in Vmax30. The effects of LTD4 and histamine on FEV1 and Vmax30 changed in parallel when the deposition of the mediators was changed to a more central pattern. This indicates that the two mediators do not differ with respect to any selective effects on different parts of the airways.

Enterohepatic circulation of N-acetyl-leukotriene E4

N-Acetyl-leukotriene E4, the end product of leukotriene C4 metabolism in the mercapturic acid pathway, was rapidly eliminated from the blood circulation into the bile of rats. Part of the N-acetyl-leukotriene E4 secreted from bile into the intestine underwent enterohepatic circulation. Leukotriene absorption occurred from the small intestine and from the colon. Biliary and urinary excretion within 5.5 h amounted to 15 and 2%, respectively, of the intraduodenally administered N-acetyl- 3H leukotriene E4 in animals anesthetized with ketamine. HPLC analyses indicated that 35% of the biliary radioactivity corresponded to unchanged N-acetyl-3H leukotriene E4, while 65% in bile and 100% in urine were polar metabolites. Enterohepatic circulation extends the biological half-life of N-acetyl-leukotriene E4.

Effects of intracoronary leukotriene D4 infusion on the coronary circulation, hemodynamics, and prostanoid release in porcine experiments

The effects of leukotriene (LT) D4 (0.5 microgram/min) infusion into the left anterior descending coronary artery (LAD) of anesthetized pigs were studied in the absence or presence of indomethacin (5 mg/kg i.v.). In some pigs, arteriocoronary venous (A-V) blood plasma concentrations of thromboxane B2 and 6-keto-prostaglandin F1 alpha were measured by RIA technique during LTD4 actions. LTD4 changed LAD blood flow at 5 and 30 s, 2, 4 and 5 min by -46% (p less than 0.01), -93% (p less than 0.001), -45% (p less than 0.01), -28% (p less than 0.05) and 16%, respectively. Thus, the coronary constriction disappeared despite sustained LTD4 infusion and was followed by reactive hyperemia. Indomethacin did not affect the coronary flow or hemodynamic responses to LTD4 infusion. The A-V difference in prostanoids did not change during LTD4 administration. Cyclooxygenase products of arachidonic acid may not be responsible for early constriction and later escape phases of LTD4 effects on the coronary circulation. However, intracoronary bolus injection of LTD4 stimulated prostacyclin release from the vasculature in a dose-dependent manner causing significant reactive hyperemia after temporary blood flow cessation. Release of a LTD4-induced vasodilating factor from the coronary vessels unrelated to prostanoids may cause escape from vasoconstriction during LTD4 infusion.

Pharmacology of aerosol leukotriene C4- and D4-induced alteration of pulmonary mechanics in anesthetized cynomolgus monkeys

Aerosol administration of solutions of 900 micrograms/ml of leukotriene C4 (LT) or D4 to cynomolgus monkeys produced dose-dependent, equipotent increases in pulmonary resistance (Rp) and decreases in dynamic lung compliance (Cdyn). Time to peak response was, in part, related to dose and ranged from 4 to 20 min. Both LTC4 and LTD4 were less potent than histamine. Aerosol pretreatment with the cyclooxygenase inhibitor indomethacin had no significant effect on either LTC4 or LTD4 dose-response curves; however, at the highest doses of these agonists a notable, nonsignificant inhibition of effects on both Rp and Cdyn was seen. Intravenous dl-propranolol had no effect on responses to LTD4. Aerosol pretreatment with FPL 55712 significantly (P less than 0.05) inhibited airway responses to both LTC4 and D4. In contrast, an intravenous infusion of FPL 55712 failed to block the bronchospastic activity of LTD4. In conclusion, cynomolgus monkeys are responsive to aerosol administration of LTC4 and LTD4, and the pharmacology of their responses appears to resemble that of man.

Airway responsiveness to leukotrienes C4 and D4 and to methacholine in patients with asthma and normal controls

Leukotrienes C4 and D4 may serve as chemical mediators in asthma. Although patients with asthma are known to be hyperresponsive to the bronchoconstrictive effects of histamine and methacholine, whether the same is true for the leukotrienes is controversial. We compared the airway responses to methacholine and to leukotrienes C4 and D4 in 12 asthmatic patients and 6 controls. We found that the patients were more responsive to the leukotrienes than the controls, and we observed a linear correlation between airway response to methacholine and that to leukotriene C4 (r = 0.68, P less than 0.01) and D4 (r = 0.79, P less than 0.001). However, relative to the airway response to methacholine, the response to the leukotrienes was much greater in the controls than in the patients. Furthermore, the asthmatic subjects who were most responsive to methacholine had the lowest relative airway response to both leukotrienes. Thus, the patients with the greatest airway responsiveness to methacholine paradoxically showed the lowest relative airway response to the leukotrienes. In contrast, this difference in relative airway responses has not been observed between methacholine and other bronchoconstrictor mediators, such as histamine. Although no adequate explanation for these observations has yet emerged, our data suggest that leukotrienes C4 and D4 are unique bronchoconstrictors with a possible role in the pathogenesis of asthma.

Comparison of cutaneous and bronchial reactivity to leukotriene D4 in humans

To establish whether a relationship exists between cutaneous and bronchial reactivity to leukotriene D4 (LTD4), endpoint cutaneous reactivity and bronchial reactivity were determined in six patients with asthma, six patients with seasonal allergic rhinitis, and six nonatopic men. In all subjects, increasing doses of LTD4 produced decreases in specific airway conductance (SGaw) and flow at 30% of vital capacity measured from a partial forced expiratory maneuver (V30P). Intracutaneous injections of LTD4 and histamine resulted in immediate wheal and erythema reactions in all patients. Serial 10-fold dilutions of LTD4 and histamine were injected to establish the lowest dose capable of producing a 4 mm wheal with erythema. Endpoint cutaneous reactivity to LTD4 ranged from 1 mumol to 100 pmol in controls and from 100 nmol to 1 fmol in patients with asthma, but statistically significant differences between groups were not apparent even with inclusion of six additional subjects. No meaningful correlations were found between the quantity of LTD4 producing the threshold cutaneous reaction and the dose of inhaled LTD4 that produced a 35% decrease in SGaw and 30% decrease in V30P. In contrast to the bronchi, where subjects in all three groups were 264 to 840 times more sensitive to LTD4 than to methacholine, 11/18 subjects (3/6 with asthma) were less sensitive to LTD4 than to histamine in terms of endpoint cutaneous reactivity. However, seven of 18 subjects who were more sensitive to LTD4 than to histamine had relative potencies ranging from 5 to 500,000.

Effect of leukotriene D4 on nasal mucosal blood flow, nasal airway resistance and nasal secretion in humans

The possible role of leukotriene D4 (LTD4) in nasal allergy was investigated in healthy volunteers. Nasal blood flow, nasal airway resistance, nasal discharge and nasal itching and sneezing were examined. LTD4 was found to induce a dose-response related increase in nasal mucosal blood flow as measured by laser-Doppler flowmetry. Histamine exhibited similar effects on blood flow in the same concentration range. Nasal airway resistance as recorded by rhinomanometry, increased in a dose-related manner after topical LTD4. Nasal secretion was obtained by nasal lavage and estimated from a dilution principle. Topical LTD4 did not increase the amount of nasal secretion, whereas a dose-related increase was found after topical histamine. LTD4 did not cause itching, sneezing or other irritative symptoms. In conclusion, LTD4 may play a role in nasal allergy by increasing blood flow and nasal airway resistance. Itching, sneezing and discharge, however, are apparently not caused by LTD4 but can be accounted for by the release of histamine or other mediators.

Evaluation of LY163443, 1-[2-hydroxy-3-propyl-4-([4- (1H-tetrazol-5-ylmethyl)phenoxy]methyl) phenyl]ethanone, as a pharmacologic antagonist of leukotrienes D4 and E4

LY163443,1-[2-hydroxy-3-propyl-4-([4- (1H-tetrazol-5-ylmethyl)phenoxy]- phenoxy]methyl)phenyl]ethanone, antagonized LTD4-induced contractions of guinea pig ileum, trachea, and lung parenchyma. Tracheal contractions to LTE4 were also inhibited by LY163443. The compound had minimal effect against ileal responses to LTC4 and parenchymal contractions to LTB4. Furthermore, LY163443 had little to no effect against contractions of isolated smooth muscles to histamine, bradykinin, PGF2 alpha, carbachol, serotonin or U46619. LY163443, given by oral administration to guinea pigs, blocked LTD4-induced increases in total pulmonary impedance (TPI). Similar responses elicited by histamine or U46619 were unaffected. Increases in TPI in response to i.v. administration of LTC4 were antagonized by LY163443 given by the same route. Ovalbumin challenge also increased TPI in guinea pigs previously sensitized against this antigen. In such animals, pretreated with pyrilamine, propranolol, and indomethacin, oral administration of LY163443 blocked the increase in TPI caused by ovalbumin. Additionally, LTD4 given intradermally to guinea pigs caused a vascular leakage which was suppressed by prior oral administration of LY163443. Finally, LY163443 relaxed isolated guinea pig trachea previously contracted with LTD4, histamine, or carbachol. Relaxation of tissues contracted by these latter two agonists suggested some inherent airway smooth muscle relaxant properties of the molecule. This was further demonstrated by showing some bronchodilator activity in an in vivo setting. Thus, this pharmacologic profile indicates that LY163443, or a member of the same chemical family, warrants consideration as a possible therapeutic agent in the treatment of asthma and in diseases characterized by an overproduction of LTD4 and LTE4.

Cardiovascular effects of leukotriene C4 and D4 in the anesthetized and conscious domestic hen

In anesthetized and conscious domestic hens i.v. injections of LTC4 (1 and 3 micrograms/hen) and LTD4 (0.1-10 micrograms/hen) induced a pronounced hypotension, initially interrupted by a small, upward pressure deflection. No significant changes in HR, ECG-characteristics, or hematocrit were observed. It is concluded that neither plasma leakage nor myocardial ischemia are likely to contribute significantly to the hypotension. Only experiments with LTD4 in conscious hens suggest a mediator function of cyclooxygenase products since the LTD4-induced hypotension was attenuated by IND. The failure of developing reflex tachycardia rather points to an impairment with manifestation of reflex mechanisms.

Aerosolized and intravenously administered leukotrienes: effects on the bronchoconstrictor potency of histamine in the guinea-pig

The effects of leukotrienes C4 and D4 (LTC4 and LTD4), administered intravenously or by aerosol, on the bronchoconstrictor potency of intravenously administered histamine have been investigated in anaesthetized, mechanically ventilated guinea-pigs. LTC4 (2 nM) had no effect on either the EC50 or the maximum contractile response to histamine on the isolated trachea of the guinea-pig. At 10 nM, LTC4 induced a rightward shift in the histamine concentration-response curve without affecting the maximum response. LTD4 (0.05-0.20 nmol kg-1, i.v.) dose-dependently enhanced histamine (9-36 nmol kg-1, i.v.)-induced increases in airways resistance, whereas equibronchoconstrictor doses of LTC4 (0.1-0.4 nmol kg-1, i.v.), failed to enhance histamine-induced increases in airways resistance. Aerosols of LTC4 and LTD4 generated from solutions of 1-16 microM and administered for 30 s, elicited concentration-dependent bronchoconstrictions comprising decreases in dynamic compliance and increases in airways resistance. At 20 min after exposure to these aerosols, the potency of histamine (9-36 nmol kg-1, i.v.) was significantly increased on both airways resistance and dynamic compliance. The potentiation induced by LTC4 (4 microM, 30 s) was maintained up to 60 min after aerosol exposure whereas that induced by LTD4 (4 microM, 30 s) was maintained up to 40 min after aerosol exposure but was not significantly different (P greater than 0.05, unpaired Student's t test) to saline-exposed animals at 60 min. LTC4 as has been previously reported for LTD4, does not enhance the histamine-induced contraction of isolated airways smooth muscle. In contrast to LTD4, intravenously administered LTC4 does not appear to enhance histamine-induced bronchoconstriction. On the other hand, aerosols of either LTC4 or LTD4 potentiate histamine in vivo in a concentration-dependent manner. These data suggest that leukotrienes may contribute to the regulation of airways reactivity to histamine in the guinea-pig.